In a liquid crystal display apparatus, an iodine- or dye-containing absorption type polarizing plate has been used commonly. Therefore, brightness (luminance) of a display surface is turned down to less than half against that of light source such as an outside light or an illuminated light. Moreover, since a liquid crystal panel of the apparatus has two pieces of the absorption type polarizing plate on a front and back (or both sides) thereof, practically, brightness of the panel reduces to 30 to 40% against that of light source. Accordingly, in order to obtain higher luminance of the panel, it is attempt to transform the polarized light to help the above-mentioned failing.
As a method for transforming a polarized light, a method using a polarizer (see, ASIA DISPLAY '95, page 731), a method for transforming the polarized light which utilizes circular polarization property of a cholesteric liquid crystal (see, ASIA DISPLAY '95, page 735) and others are exemplified. However, in the method using the prism, the polarized light depends on an angle or a wavelength thereof, and furthermore the obtained apparatus is short in lightness of weight or compactness thereof. In the case where the cholesteric liquid crystal is used, it is necessary that the liquid crystal comprises multi layers differing in spiral pitch to cover throughout a range of wavelength. However, in such a case, it is complicated and costly to produce such a liquid crystal.
Japanese Patent Application Laid-Open No. 333428/1995 (JP-7-333428A) discloses a scattered type polarizing sheet which comprises a tabular element composed of a birefringent substance and an optical element composed of a synthetic resin, and the optical elements are laminated on the both sides of the tubular element. However, since the sheet uses a single tabular element (calcite), the sheet is restricted in producible size thereof and is expensive.
Japanese Patent Application Laid-Open No. 506985/1997 (JP-9-506985A) discloses an optical display apparatus or device comprising a polarizer which is obtained by multi-laminating films composed of a polyester-series resin and the like. However, also, it is complicated and expensive to produce the polarizer since the laminate composed of hundreds of thin layers is stretched for obtaining the polarizer.
A method using a complex of a liquid crystal and a polymer has been known [Japanese Patent Application Laid-Open No. 76114/1996 (JP-8-76114A), Japanese Patent Application Laid-Open No. 274108/1997 (JP-9-274108A), Japanese Patent Application Laid-Open No. 221688/1998 (JP-10-221688A), and U.S. Pat. No. 4,688,900]. However, the liquid crystal is expensive.
Japanese Patent Application Laid-Open No. 297204/1997 (JP-9-297204A) discloses an anisotropic scattering or diffusing element dispersed and aligned an inorganic scattering particle in a polymer or resin. However, in the case of aligning the scattering particle to a constant direction, the element is apt to generate a void(s) between the polymer and the inorganic particle, and as a result the element can not be produced stably. Incidentally, as a processing method in which the void is not generated easily, it is adopted that a method in which a polymer is subjected to ultraviolet to cure, with aligning an inorganic particle in the polymer by calendering with use of a roller. However, the polymer used in the method is limited.
U.S. Pat. No. 4,871,784 discloses a method which comprises stretching a sheet dispersed a second polymer in a first polymer to generate a microvoid. However, in the method to generate an elliptical microvoid around the dispersoid, the microvoid has various geometrical structures in the interface. Therefore, it is difficult to control polarizing properties of the sheet.
Japanese Patent Application Laid-Open No. 506990/2000 (JP-2000-506990A) discloses a method for stretching a sheet dispersed a second polymer in a first polymer. As a combination of the first polymer with the second polymer, the literature describes a combination of 2,6-polyethelene naphthalene with polymethylmethacrylate or syndiotactic polystyrene. Moreover, the literature describes that a small amount of naphthalenedicarboxylic acid can be utilized in order to improve interphase adhesiveness, and a compatibilizing agent is used in order to form a void. However, when the sheet dispersed the second polymer in the first polymer is stretched, it is impossible to produce the obtained sheet stably because of weakness of the bonding force (associative strength) between the above two polymers, and generation of a slight amount of voids between a continuous phase and a dispersed phase (or discontinuous phase or dispersoid) thereof with stretching. Moreover, the literature describes an embodiment using polystyrene glycidylmethacrylate compatibilizing agent as the compatibilizing agent. However, in such an embodiment, it is impossible to obtain a sheet having stability, and excellent flatness or smoothness of external appearance, because of rapid increase in viscosity and gelation on the end of the agent.